This Phase I SBlR project addresses the need for a body-powered voluntary- closing (VC) prosthetic prehensor offering variable mechanical advantage (VMA) and passive gripping assist. In this three-phase program, a unique VC design will be developed to potentially assist thousands of individuals for whom existing prehensor designs are unsuitable. VC prehensors have long been desired for their natural and intuitive operation, and their ability to promote proprioception. Unfortunately, engineering difficulties have prevented the creation of practical designs. Using a synergetic combination of VMA and holding assist mechanisms, the proposed device solves the problems of high control cable tension and grip-lock, characteristics that have prevented widespread acceptance of VC prehension. In Phase I, a prototype will be designed, fabricated, and tested to show that it 1) changes mechanical advantage and locks appropriately, 2) requires less work to use than do existing voluntary opening (VO) devices, and 3) performs reliably. Limited field-testing by amputees will provide key feasibility information needed for Phase II optimization and full-scale development and Phase III commercialization. Creation of new opportunities to rehabilitate and restore key physical capabilities for thousands of individuals with upper-limb traumatic injuries, diseases, or birth defects is the primary goal of this R&D project. PROPOSED COMMERCIAL APPLICATIONS: The proposed prehensor device addresses a clear unmet need for a practical body-powered, voluntary-closing gripping device. Between 30,000 and 50,000 individuals in the U.S alone desire restored gripping capability, but existing commercial devices do not work or are inadequate. Given the option of using a practical VC prehensor, many individuals would switch, and others who do not use grippers would start, expanding the market further.